Electronic signals are carried by electrical current through conductors and transistors in a large scale IC die fabricated on a semiconductor wafer. The energy carried by the electrical current in an IC die is partially dissipated along the paths of current flow through the IC in the form of heat. The heat generated, P, in an IC is the sum of dynamic power, PD, and static power, PS:P=PD+PS=ACV2f+VIleak 
where A is the gate activity factor, C is the total capacitance load of all gates, V2 is the peak-to-peak supply voltage swing, f is the frequency, and Ileak is the leakage current. The static power term, PS=VIleak, is the static power dissipated due to leakage current, Ileak. The dynamic power term, PD=ACV2f, is the dynamic power dissipated from charging and discharging the IC's capacitive loads.
Another characteristic of IC die is the uneven distribution of temperature on the die. More and more functional blocks are integrated in a single die in system-on-chip (SOC) designs. Higher power density blocks create an uneven temperature distribution and lead to “hotspots,” also known as “hot blocks,” on the die. Hotspots can lead to a temperature difference of about 5° C. to roughly 30° C. across a die. Since carrier mobility is inversely proportional to temperature, the clock speed is typically designed for the hottest spot on the die. Consequently, thermal design is driven by the temperature of these on-die hotspots. Also, if uniform carrier mobility is not achieved across the IC die due to on-chip temperature variations across the die, this may result in variations in signal speed and in complicating circuit timing control.
Heat spreaders, including drop-in heat spreaders, heat sinks, and heat pipes have been used in the past to enhance thermal performances of IC packages. In addition, another known approach is attaching a high thermal conductivity lid directly to the backside of the die to improve heat spreading. A significant problem with known practices is that the frontside of the die where the hot spots are located (e.g., near where transistors switching takes place) must be used for wiring and the heat generated during operation must be channeled out through the full thickness of the substrate of the IC die to its bottomside before being connected to heat dissipation means, and are thus inefficient at dissipating heat.